1. Field of the Invention
The present invention relates to a method for producing L-tryptophan by fermentation, and particularly relates to a method for producing L-tryptophan by fermentation using Coryneform glutamic acid-producing bacteria constructed by a gene-recombination technique.
2. Description of the Prior Art
When L-tryptophan is to be produced by fermentation, artificial mutation has been given to wild strains to impart L-tryptophan productivity to them because wild strains hardly produce L-tryptophan outside their cells.
As previously known artificial mutants having L-tryptophan productivity, there can be cited mutants of the genus of Brevibacterium, Microbacterium or Corynebacterium that are resistant to 5-methyltryptophan mutants of the genus Corynebacterium that require tyrosine and phenylalanine for growth and are resistant to phenylalanine antagonists (Japanese Patent Publication No. 19037/1976), mutants of the genus of Bacillus that are resistant to 5-fluorotryptophan (Japanese Patent Laid-Open No. 85289/1974) and mutants of the genus of Brevibacterium that are resistant to 5-methyltryptophan and to m-fluorotryptophan (Japanese Patent Laid-Open No. 42091/l975).
On the other hand, recently some reports have been made on trials of construction of L-tryptophan-producing bacteria using a gene recombination technique different from the above-mentioned artificial mutation technique. For example, it was reported in Appl. Environ. Microbiol. 38, (2), 181-190 (1979) that the specific mutants of Escherichia coli that contained a plasmid having trp E 472 genes of Escherichia coli produced about 1.3 g/l of L-tryptophan. In addition, it was also mentioned in Proceedings of 1980 Annual Meeting of the Society of Fermentation Technology, Japan, page 170 that mutants of Escherichia coli containing a plasmid having the tryptophan operons of Escherichia coli produced 360 mg/l of L-tryptophan.
Although several high tryptophan-producers have been known among the mutants of Coryneform glutamic acid-producing bacteria as mentioned above, there has been no significant trial so far as the inventors know to construct tryptophan-producer using such Coryneform-bacteria as above which have high potential ability to produce L-tryptophan.
A need, therefore, continues to exist for a more efficient method for producing L-tryptophan by fermentation.